Middle Cretaceous back-arc formation and arc evolution along the Asian margin: the Shyok Suture Zone in northern Ladakh (NW Himalaya)
Middle Cretaceous back-arc formation and arc evolution along the Asian margin: the Shyok Suture Zone in northern Ladakh (NW Himalaya)
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DOI：
10.1016/s0040-1951(00)00135-9
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发表时间：
2000-10
期刊：
影响因子：
2.9
通讯作者：
Y. Rolland;A. Pêcher;C. Picard
中科院分区：
文献类型：
--
作者：
Y. Rolland;A. Pêcher;C. Picard
拉达克古火山弧的Shyok缝合带是由侵入花岗闪长质岩体的白垩纪火山-沉积建造组成的。野外观察表明，不同火山弧和弧后环境的岩石单元具有构造叠加的特征。在西部（Skardu地区），Shyok缝合带可细分为两组：（1）北方群，由玄武岩和凝灰岩组成。玄武岩的LREE亏损与LILE富集和轻微的Nb亏损表明弧后盆地的起源。(2)南部群主要由安山岩组成，表现为LREE富集，HREE模式平坦，Nb-Ta亏损强烈，LILE富集。南部群的火山岩似乎有岛弧拉斑玄武岩（IAT）的钙碱性亲和力。在缝合带的东部（Nubra-Shyok地区），Albian至Cenomanian时代的硅质沉积物占主导地位。这些沉积物对应于拉达克弧北方的一个大型碎屑台地。在顶部，这些沉积物与玄武质到安山质熔岩夹层。这些熔岩似乎是更多的分化和钙碱性的性质比斯卡杜南部集团熔岩，但表现出类似的火山弧的亲和力。在该地区没有发现弧后盆地的证据。我们从这两个地区获得的数据显示，拉达克北方地区的构造从弧后构造向弧后构造演化为西北-东南向构造。该弧后盆地的开启发生在拉达克弧的西北侧。这个后弧逐渐向东关闭。弧本身在东部更成熟，类似于西藏南部的大陆弧，其特征是更多的大陆沉积。随后的喜马拉雅期构造变质演化、弧后盆地的闭合和沿着Shyok缝合线的变形，反映了亚洲边缘和科希斯坦-拉达克弧沿着的早期不对称几何形状。
The Shyok Suture Zone of the Ladakh palaeovolcanic arc is made of Cretaceous volcanosedimentary formations intruded by granodioritic plutons. Field observations show a tectonic stacking of litho-units from different volcanic arc and back-arc environments. In the western part (Skardu area), the Shyok Suture Zone can be subdivided into two groups: (1) The Northern Group, which consists of olistolith basaltic blocks and tuffs. The basalts are LREE depleted with a LILE enrichment and a slight Nb depletion suggesting a back-arc basin origin. (2) The Southern Group, which consists predominantly of andesites that show LREE enrichment, a flat HREE pattern, strong Nb–Ta depletion, and LILE enrichment. The volcanic rocks of the Southern Group appear to have island-arc tholeiite (IAT) to calc-alkaline affinities. In the eastern part of the suture zone (Nubra–Shyok area), Albian to Cenomanian age silicoclastic sediments predominate. These sediments correspond to a large detrital platform built on the northern part of the Ladakh Arc. At the top, these sediments interlayer with basaltic to andesitic lavas. These lavas appear to be more differentiated and calc-alkaline in nature than the Skardu Southern Group lavas, but show similar volcanic arc affinities. No evidence of a back-arc basin was found in this area. Our data from these two areas shows a northwest–southeast evolution, from back-arc to arc formations in northern Ladakh. Opening of this back-arc basin occurred on the northwestern side of the Ladakh Arc. This back-arc was progressively closing eastward. The arc itself was more mature in the east, resembling the southern Tibetan continental arc, and was characterised by more continental sedimentation. Subsequent Himalayan tectonometamorphic evolution, closure of the back-arc basin and deformation along the Shyok Suture, reflects an early asymmetrical geometry along the Asian margin and Kohistan–Ladakh Arc.